| Autor: |
Bertrand, Jean-Michel, Michard, Annie, Boullier, Anne-Marie, Dautel, Danielle |
| Zdroj: |
Tectonics; 1986, Vol. 5 Issue 7, p955-972, 18p |
| Abstrakt: |
Discovery of large-scale deep-seated thrusts in Central Hoggar, with a plurifacial evolution ranging from lower amphibolite facies to upper greenschist facies conditions and linked to a regional refoliation, has led us to reconsider the Pan-African tectonic and metamorphic history in that region. Two areas are described, and a review of other thrusts leads to an interpretative cross section of a large portion of reactivated continental crust. The age and kinematics of this structural reworking have been approached using U/Pb zircon dating in the Tamanrasset region. Despite the difficulty of estimating the age of the initiation of the assumed intracontinental A-type subduction, the results provide a time span of 30-40 m.y. between the climax of granitoid emplacement and a late retrogressive offset along the thrust planes. Some key ages were determined: (1) 2075 ± 30 Ma is the age given by granulite facies remnants which escaped from the refoliation, the corresponding lower intercept at 530 ± 70 Ma confirms the Pan-African imprint; (2) 615 ± 5 Ma reflecting the age of syntectonic to late-tectonic granitoids emplaced in reworked gneisses and in preserved granulites; (3) 580 Ma, the concordant age of sphenes and monazites from the same granitoids, which is interpreted as corresponding to the end of medium-grade conditions. No evidence has been found of a ∼1000 Ma age: a Kibaran event does not appear to exist in Central Hoggar. The age similarity between the observed deep intracontinental evolution of Central Hoggar and the collision-related tectonics of Western Hoggar and Iforas suggests a common origin for both phenomena. [ABSTRACT FROM AUTHOR] |
| Databáze: |
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